Add Service Workers

**https://github.com/TalAter/awesome-service-workers**

*A service worker is an event-driven worker registered against an origin and a path. It takes the form of a JavaScript file that can control the web page/site it is associated with, intercepting and modifying navigation and resource requests, and caching resources in a very granular fashion to give you complete control over how your app behaves in certain situations (the most obvious one being when the network is not available.)*

- [x] I have read and understood the [contribution guidelines](https://github.com/sindresorhus/awesome/blob/master/contributing.md) and the [instructions for creating a list](https://github.com/sindresorhus/awesome/blob/master/create-list.md).
- [x] This pull request has a descriptive title. *(For example: `Add Node.js`)*
- The list I added
	- [x] **has been around for at least 20 days,**
	- [x] is not a duplicate,
	- [x] only has awesome items with descriptions *(Awesome lists are curations of the best, not of everything)*,
	- [x] contains the [awesome badge](https://github.com/sindresorhus/awesome/blob/master/awesome.md#awesome-badge) on the right side of the list heading,
	- [x] has a `Table of Contents` as the first section,
	- [x] has an [appropriate license](https://github.com/sindresorhus/awesome/blob/master/awesome.md#choose-an-appropriate-license) *(Meaning something like CC0, NOT a code licence like MIT, BSD, Apache, etc)*,
	- [x] has [contribution guidelines](https://github.com/sindresorhus/awesome/blob/master/awesome.md#include-contribution-guidelines),
	- [x] has been checked for inconsistent formatting, spelling, and grammar *(This includes starting each link description with an uppercase character and ending it with a dot, and consistent naming)*,
	- [x] has been added at the bottom of the appropriate category.

Closes #706

readme.md

@@ -179,6 +179,7 @@ Check out my [blog](https://blog.sindresorhus.com) and follow me on [Twitter](ht
 - [Chrome DevTools](https://github.com/ChromeDevTools/awesome-chrome-devtools)
 - [PostCSS](https://github.com/jjaderg/awesome-postcss)
 - [Draft.js](https://github.com/nikgraf/awesome-draft-js) - Rich text editor framework for React.
+- [Service Workers](https://github.com/TalAter/awesome-service-workers)
 
 
 ## Back-End Development